HDR Test Highlights Red Bull Crashed Ice Production
Grass Valley sees 1080p format with HLG as step toward next-gen broadcasting
The Red Bull Crashed Ice Championship recently held in Saint Paul, MN, provided an opportunity for Grass Valley, Red Bull Media, and Lyon Video to test the waters of 1080p HDR production.
“I was very pleased with how smooth it worked [even though] the camera shaders had no previous experience with HDR,” says Klaus Weber, senior product marketing manager, cameras, Grass Valley. “At this point, we have a fully developed system with all the bells and whistles.”
Lyon Video was on hand with production-truck support, and technical changes to the truck included installation of 6RU worth of HDR-to-SDR conversion cards (XVP-3901) and SDR-to-HDR upconversion cards (UHD-3901-C).
Grass Valley provided HDR licenses to Red Bull for approximately 10 HDR-capable cameras used during the tests. All the LDX86 cameras were running at 1080p/59.94 with wide-color-gamut hybrid log gamma (HLG) standard. Two high-speed cameras operated in 1080p with 2020 color space (converted to HLG) while POV cameras shot at 1080i in REC-709 color space that had to be converted to HLG. The non-HDR cameras held up well once upconverted via the Grass Valley UHD-3901-UC, the only issue being that the POV cameras were 1080i so there was a bit of a hit.
“Those were used for special shots like being mounted directly on the track and providing a completely different view,” Weber explains. “So no one really noticed the difference.”
One challenge was lighting at the event: the temperature of the main stadium lighting was close to 5000K, and supplemental light sources at the side of the ice track were 2500K-3000K. That combination meant that the center of the ice track tended to have a bluish tint while the sides were bathed in a yellowish light.
“It looked nice, but it was not natural,” Weber points out. He adds that color accuracy is easy in a natural scene — “Everyone knows what the grass should look like” — but not so much with bluish or yellowish lighting.
The final production format was HDR 2020 at 1080p resolution; the main distribution format, 1080p with 709 color space. Given that most viewers at home would not see the HDR product, the camera shaders worked with a downconverted SDR signal so that they would shade to best meet viewer needs.
“As long as the SDR is shaded correctly, the HDR is more forgiving,” says Weber.
That is because the entire SDR range of contrast ratio lies within the HDR range so that, no matter how extreme the shading would be, it would be fine on an HDR set. But shading in HDR for SDR means that the contrast could possibly fall outside the SDR range, leading to issues like clipping.
“In some years, when there are more HDR viewers, there might be a change in philosophy,” says Weber. “But, with nearly 100% of viewers watching in SDR, you can’t accept any compromises.”
The up/downconverters were used not only for the cameras but also for graphical elements created in 709 color space.
“We needed approximately 10 cards each for upconversion and downconversion, and that required 6RU of electronics,” says Weber. “The conversion of a 1080p SDR truck into HDR could be done by only adding six or nine racks of electronics.”
Getting the Lyon Video truck ready took about two days, and one factor in that quick turnaround was the use of HLG.
“HLG is backwards-compatible. All of the monitors, except for the main one, were original monitors with multiviewers up/down converting perfectly,” says Weber. “In PQ [format], things get more complex because every monitor needs to be PQ-capable.”
Grass Valley has been doing a lot of testing with broadcasters in Europe and the U.S., he says, noting that commercial broadcasters in Europe are interested in a 4K HDR experience while the U.S. broadcasters and several of the European public broadcasters are looking at 1080p.
“The 1080p format with HLG could be a very cost-efficient upgrade path to next-generation broadcasting.”